Scintillator having integrated collimator and method of manufacturing same

ABSTRACT

The present invention is directed to an integrated scintillator and collimator array for a CT detector. The integrated scintillator and collimator are fabricated from a manufacturing process or technique whereupon an array of scintillator material is positioned on a tooling base such that a collimator mold housing having a collimator mold therein may be positioned on the block of scintillator material. The block and mold housing are then aligned allowing a collimator mixture to be disposed into the mold. The collimator mixture is then allowed to cure to form an integrated scintillator and collimator.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is continuation of and claims priority of U.S.Ser. No. 10/249,699 filed Apr. 30, 2003, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to diagnostic imaging and, moreparticularly, to an integrated scintillator and collimator and method ofmanufacturing same.

Typically, in computed tomography (CT) imaging systems, an x-ray sourceemits a fan-shaped beam toward a subject or object, such as a patient ora piece of luggage. Hereinafter, the terms “subject” and “object” shallinclude anything capable of being imaged. The beam, after beingattenuated by the subject, impinges upon an array of radiationdetectors. The intensity of the attenuated beam radiation received atthe detector array is typically dependent upon the attenuation of thex-ray beam by the subject. Each detector element of the detector arrayproduces a separate electrical signal indicative of the attenuated beamreceived by each detector element. The electrical signals aretransmitted to a data processing system for analysis which ultimatelyproduces an image.

Generally, the x-ray source and the detector array are rotated about thegantry within an imaging plane and around the subject. X-ray sourcestypically include x-ray tubes, which emit the x-ray beam at a focalpoint. X-ray detectors typically include a collimator for collimatingx-ray beams received at the detector, a scintillator for convertingx-rays to light energy adjacent the collimator, and photodiodes forreceiving the light energy from the adjacent scintillator and producingelectrical signals therefrom.

As stated above, typical x-ray detectors include a collimator forcollimating x-ray beams such that collection of scattered x-rays isminimized. As such, the collimators operate to attenuate off-anglescattered x-rays from being detected by a scintillator cell. Reducingthis scattering reduces noise in the signal and improves the finalreconstructed image. Therefore, it is necessary that the scintillatorarray and the collimator, typically plates extending along one dimensionabove the scintillator array, are uniformly aligned. That is, exactmechanical alignment is required between the collimator plates and thecast reflector lines in the array of scintillators.

Known manufacturing processes attempt this exact alignment byconstructing a continuous collimator that is sized to dimensionallymatch the width and length of the entire detector array. That is, thecollimator plates are arranged or arrayed in a continuous consistentpattern or pitch that spans the entire detector length and is placed andattached to the detector rail structure. As such, individualscintillator arrays or packs are must then be exactly aligned to thecontinuous collimator to ensure that all scintillator cells andcollimator cells are aligned exactly; otherwise the collimator must bediscarded or repaired, or the scintillator packs must be discarded. Thisprocess requires excessively tight tolerancing and requires greatoperator skill and patience to assemble. Accordingly, these knownprocesses are susceptible to waste of parts, material, and labor.

Additionally, as CT detectors grow in the z-direction, alignmentrequirements will tighten and the number of cells requiring alignmentwill increase. Therefore, the low process yields and high-end processscrap and re-work associated with these known manufacturing processeswill increase the cost and time associated with CT detector assembly.

Notwithstanding the advances made in CT detector manufacturing, theseknown detector assemblies and assembly processes result in a detectorwith less than optimal collimation.

Referring to FIG. 10, a known CT detector 1 fabricated according toknown manufacturing processes is shown. The CT detector 1 includes aseries of tungsten collimator plates 2 that collimate x-rays projectedtoward scintillator cells 3 of a scintillator array 4. As shown, each ofthe collimator plates 2 is generally aligned with a reflector line 5disposed between adjacent scintillators 3. The reflector lines 5 preventlight from being emitted between adjacent scintillators. Thescintillator array is coupled to a photodiode array 6 that detects lightemissions from the scintillator array and transmits correspondingelectrical signals to a data acquisition system for signal processing.As readily shown, the collimator plates are not integrated with theindividual scintillator elements 3. That is, an air gap 7 exists betweenthe collimator plates and the scintillator cells 3. The air gap 7typically results in a separation between the collimator plates and thescintillator array of approximately two to four thousands of an inch.This air gap occurs as a result of the manufacturing process whereuponthe collimator plates are formed as a single collimator assembly thataccepts and aligns an array of scintillators. The air gap, however,makes the CT detector susceptible to x-rays received between twocollimator plates impinging upon an adjacent scintillator therebyresulting in undesirable anomalies in the final reconstructed CT image.

Therefore, it would be desirable to design an integrated scintillatorand collimator absent the aforementioned air gap as well as a method ofmanufacturing such an integrated scintillator and collimator.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is directed to an integrated scintillator andcollimator and method of manufacturing same that overcome theaforementioned drawbacks. The integrated scintillator and collimatorreduces x-ray cross-talk between adjacent detector cells and improvesdimensional alignment between collimator septum and scintillatorreflector walls by integrating collimator plates with a top reflectorsurface of a scintillator. A pixilated array of scintillators is placedon a tooling base whereupon a mold having a series of parallel alignedair cavities is positioned atop the array of scintillators. The aircavities within the mold are positioned such that each aligns with areflector line in the scintillator array. Using high precision tooling,the mold and the scintillator array are precisely aligned relative toone another. Upon proper alignment, a vacuum pump is used to remove theair cavities from within the mold. Thereafter, an injector is used todispose collimator mixture within the mold and which is allowed to cure.Once the collimator mixture has cured, the integratedscintillator/collimator is formed.

Therefore, in accordance with one aspect of the present invention, amethod of manufacturing a detector having an integrated scintillator andcollimator is provided. The method includes the steps of positioning anarray of scintillator elements or pack on a tooling base and positioninga collimator mold housing having a collimator mold cavity therein on theblock. As a result, the mold cavity will be very accurately aligned tothe scintillator array pattern. A collimator mixture is then disposedinto the mold cavity and allowed to cure to form an integratedscintillator and collimator.

In accordance with another aspect of the present invention, a detectorfor a CT system includes an array of scintillation elements arranged toconvert received x-rays to light. A plurality of collimator elements isintegrally formed in a top surface of the array of scintillationelements and operates to attenuate off-angle scattered x-rays from beingdetected by scintillator elements. The detector further includes anarray of photodiode elements arranged to receive light emissions fromthe array of scintillation elements.

According to another aspect of the present invention, an integratedscintillator and collimator array is formed by the steps of placing anarray of pixilated scintillators on a tooling base and positioning acollimator mold defining a plurality of cavities that extend to a topsurface of the array adjacent the array. A collimator material is thendisposed within the plurality of cavities and cured so as to form theintegrated scintillator and collimator array.

In accordance with yet another aspect of the present invention, anapparatus for manufacturing an integrated scintillator and collimatorincludes a tooling base designed to support a block of scintillatingmaterial and a mold to be positioned on the block of scintillatingmaterial. An alignment mechanism is provided to align the block in themold in an aligned arrangement as well as a mold evacuator designed toremove air cavities within the mold. A collimator mixture supply is alsoprovided to supply collimator material to the mold.

According to yet another aspect of the present invention, a system tomanufacture an integrated scintillator/collimator includes means forpositioning a block of scintillator pack on a tooling base as well asmeans for positioning a collimator mold over the block. Means foraligning the block and the collimator mold is provided as well as meansfor removing air cavities from the mold. The system also includes meansfor disposing collimator material into a volume previously occupied bythe removed air cavities and means for curing the collimator material toform an integrated scintillator and collimator.

Various other features, objects and advantages of the present inventionwill be made apparent from the following detailed description and thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate one preferred embodiment presently contemplatedfor carrying out the invention.

In the drawings:

FIG. 1 is a pictorial view of a CT imaging system.

FIG. 2 is a block schematic diagram of the system illustrated in FIG. 1.

FIG. 3 is a perspective view of one embodiment of a CT system detectorarray.

FIG. 4 is a perspective view of one embodiment of a detector.

FIG. 5 is illustrative of various configurations of the detector in FIG.4 in a four-slice mode.

FIG. 6 is a cross-sectional schematic diagram of a detector inaccordance with the present invention.

FIG. 7 is a cross-sectional schematic diagram of an assembly tomanufacture an integrated scintillator and collimator in accordance withthe present invention.

FIG. 8 is a pictorial view of a CT system for use with a non-invasivepackage inspection system.

FIG. 9 is a flow chart setting forth the steps of a manufacturingprocess or technique for forming an integrated scintillator/collimatorin accordance with the present invention.

FIG. 10 is a cross-sectional schematic diagram of a known detector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The operating environment of the present invention is described withrespect to a four-slice computed tomography (CT) system. However, itwill be appreciated by those skilled in the art that the presentinvention is equally applicable for use with single-slice or othermulti-slice configurations. Moreover, the present invention will bedescribed with respect to the detection and conversion of x-rays.However, one skilled in the art will further appreciate that the presentinvention is equally applicable for the detection and conversion ofother high frequency electromagnetic energy. The present invention willbe described with respect to a “third generation” CT scanner, but isequally applicable with other CT systems.

Referring to FIGS. 1 and 2, a computed tomography (CT) imaging system 10is shown as including a gantry 12 representative of a “third generation”CT scanner. Gantry 12 has an x-ray source 14 that projects a beam ofx-rays 16 toward a detector array 18 on the opposite side of the gantry12. Detector array 18 is formed by a plurality of detectors 20 whichtogether sense the projected x-rays that pass through a medical patient22. Each detector 20 produces an electrical signal that represents theintensity of an impinging x-ray beam and hence the attenuated beam as itpasses through the patient 22. During a scan to acquire x-ray projectiondata, gantry 12 and the components mounted thereon rotate about a centerof rotation 24.

Rotation of gantry 12 and the operation of x-ray source 14 are governedby a control mechanism 26 of CT system 10. Control mechanism 26 includesan x-ray controller 28 that provides power and timing signals to anx-ray source 14 and a gantry motor controller 30 that controls therotational speed and position of gantry 12. A data acquisition system(DAS) 32 in control mechanism 26 samples analog data from detectors 20and converts the data to digital signals for subsequent processing. Animage reconstructor 34 receives sampled and digitized x-ray data fromDAS 32 and performs high speed reconstruction. The reconstructed imageis applied as an input to a computer 36 which stores the image in a massstorage device 38.

Computer 36 also receives commands and scanning parameters from anoperator via console 40 that has a keyboard. An associated cathode raytube display 42 allows the operator to observe the reconstructed imageand other data from computer 36. The operator supplied commands andparameters are used by computer 36 to provide control signals andinformation to DAS 32, x-ray controller 28 and gantry motor controller30. In addition, computer 36 operates a table motor controller 44 whichcontrols a motorized table 46 to position patient 22 and gantry 12.Particularly, table 46 moves portions of patient 22 through a gantryopening 48.

As shown in FIGS. 3 and 4, detector array 18 includes a plurality ofscintillators 57 forming a scintillator array 56. A collimator (notshown) is positioned above scintillator array 56 to collimate x-raybeams 16 before such beams impinge upon scintillator array 56.

In one embodiment, shown in FIG. 3, detector array 18 includes 57detectors 20, each detector 20 having an array size of 16×16. As aresult, array 18 has 16 rows and 912 columns (16×57 detectors) whichallows 16 simultaneous slices of data to be collected with each rotationof gantry 12.

Switch arrays 80 and 82, FIG. 4, are multi-dimensional semiconductorarrays coupled between scintillator array 56 and DAS 32. Switch arrays80 and 82 include a plurality of field effect transistors (FET) (notshown) arranged as multi-dimensional array. The FET array includes anumber of electrical leads connected to each of the respectivephotodiodes 60 and a number of output leads electrically connected toDAS 32 via a flexible electrical interface 84. Particularly, aboutone-half of photodiode outputs are electrically connected to switch 80with the other one-half of photodiode outputs electrically connected toswitch 82. Additionally, a reflector layer (not shown) may be interposedbetween each scintillator 57 to reduce light scattering from adjacentscintillators. Each detector 20 is secured to a detector frame 77, FIG.3, by mounting brackets 79.

Switch arrays 80 and 82 further include a decoder (not shown) thatenables, disables, or combines photodiode outputs in accordance with adesired number of slices and slice resolutions for each slice. Decoder,in one embodiment, is a decoder chip or a FET controller as known in theart. Decoder includes a plurality of output and control lines coupled toswitch arrays 80 and 82 and DAS 32. In one embodiment defined as a 16slice mode, decoder enables switch arrays 80 and 82 so that all rows ofthe photodiode array 52 are activated, resulting in 16 simultaneousslices of data for processing by DAS 32. Of course, many other slicecombinations are possible. For example, decoder may also select fromother slice modes, including one, two, and four-slice modes.

As shown in FIG. 5, by transmitting the appropriate decoderinstructions, switch arrays 80 and 82 can be configured in thefour-slice mode so that the data is collected from four slices of one ormore rows of photodiode array 52. Depending upon the specificconfiguration of switch arrays 80 and 82, various combinations ofphotodiodes 60 can be enabled, disabled, or combined so that the slicethickness may consist of one, two, three, or four rows of scintillatorarray elements 57. Additional examples include, a single slice modeincluding one slice with slices ranging from 1.25 mm thick to 20 mmthick, and a two slice mode including two slices with slices rangingfrom 1.25 mm thick to 10 mm thick. Additional modes beyond thosedescribed are contemplated.

Referring now to FIG. 6, a CT detector having an integrated scintillatorand collimator is schematically shown. The detector 20 includes aphotodiode array 52 coupled to receive light emissions from ascintillator array 56 of scintillation elements 57. Cast directly ontothe scintillation array or pack is a plurality of collimator plates 86.The collimator plates 86 are precisionally aligned with reflector lines88 disposed between the scintillator elements 57. By casting thecollimator plates directly onto the scintillator pack, the air gapdiscussed with reference to FIG. 10 is eliminated thereby improving thecollimation achieved by collimator plates 86. As will be described ingreater detail below, each of the collimator plates is formed by acombination or mixture of tungsten and epoxy.

Casting the collimator plates directly onto a top reflective surface 90of the scintillator pack improves the rigidity of thescintillator/collimator structure thereby improving the detector'sresponse to loads induced by a rotating gantry during CT dataacquisition. That is, the collimator plates of a CT detector 1 similarto that shown in FIG. 10 are susceptible to gravitational and rotationalforces induced movement as a result of the collimator plates beingseparated from the scintillator array by the previously discussed airgap. The CT detector illustrated in FIG. 6, however, has reducedsusceptibility to the aforementioned gravitational forces as a result ofthe collimator plates being directly cast onto the scintillator pack.

Referring now to FIG. 7, a tooling assembly 92 for manufacturing anarray of integrated scintillators and collimators is shown. The toolingassembly includes a tooling base 94 designed to support a scintillatorarray cast pack 96 that is positioned within the lower mold cavity 98.The lower mold cavity 98 is aligned with an upper mold housing 100 suchthat the pack 96 and mold 102 are properly aligned with respect to oneanother. To ensure proper and precisioned alignment, tooling assembly 92includes a dowel pin alignment assembly 104. Other dowel pins andalignment tools such as bore datums (not shown) are contemplated andapplicable with the illustrated assembly.

In the illustrated embodiment, mold 102 includes a series of cavities106 that is uniformly aligned in parallel relative to cast pack 96.Further, each cavity 106 has a height equal to the desired height of acollimator plate and extends to the top surface 108 of scintillatorarray cast pack 96.

Assembly 92 further includes an evacuation gate 110 that is connected toa vacuum pump 112. The vacuum pump is controlled by a CPU 114 to removeair from each cavity 106. When the mold is positioned atop thescintillator pack, air fills cavities 106. This air must be removed forproper formation of the collimator, as will be described hereinafter. Assuch, pump 112 is used to remove air from cavities 106. After a vacuumis formed within the mold housing 100, a collimator mixture is injectedby injector 116 through fill gate 118 such that each of the cavities 106is filled with collimator mixture. The collimator mixture may directlyinjected by injector 116 or drawn into the mold cavity by the vacuumcreated in the cavity upon removal of air from within the cavity. Thecollimator mixture is preferably a combination of tungsten and epoxy.Additionally, the collimation is preferably a powder. However, othercombinations, mixtures, and combinations and in non-powder forms may beequivalently used. The collimator mixture is cured at room temperatureor elevated temperatures within the mold housing 100. Once cured, themold housing is removed thereby leaving a series of collimator platesintegrally formed with a top surface of the scintillator pack.

Referring now to FIG. 8, a manufacturing process 120 for manufacturingan integrated scintillator and collimator array begins at 122 with aseries of diced slices of scintillator material undergoing a hot settingprocess at 124. After undergoing the hot setting process 124, a mold orfence is installed at 126. The mold is used to properly disposereflector material between each scintillation element. The material usedto form the reflector layer is allowed to cast and cure 128 whereuponthe mold is removed at 130. The resulting scintillator array cast packhaving the reflector lines integrated therewith is milled at 132.

Following milling of the top reflective layer of the cast pack, acollimator cavity is positioned about the milled scintillator pack at134. As stated above, the mold cavity is used during aligning of thescintillator pack relative to the collimator mold. Once the mold cavityand scintillator pack are properly positioned on a tooling base, acollimator mold is positioned or installed relative to the scintillatorpack and mold cavity at 136. The collimator mold cavity and scintillatorpack are properly aligned using a dowel pin alignment assembly and aseries of bore datums, as was previously described. Once the mold,cavity, and block are properly aligned, the air contained in each of thecavities, as a result of the positioning of the mold on the scintillatorpack, is removed using a vacuum pump. Once a vacuum is created withinthe mold, the collimator mixture or powder is introduced into each ofthe cavities 138. The injected mixture is then allowed to cure 140thereby resulting in a series of collimator plates being formedintegrally with a top surface of the scintillator pack. The moldassembly is then disassembled at 142 resulting in an array of integratedscintillators and collimators. The resulting assembly then undergoes agrinding, inspection, and testing stage 144 to ensure proper alignmentand fabrication of the integrated scintillator and collimator array 144.

The present invention has been described with respect to fabrication ofintegrated scintillator and collimator for a CT detector of a CT imagingsystem. CT detectors incorporating an integrated scintillator andcollimator in accordance with the present invention may be used inmedical imaging systems as well as parcel inspections systems similar tothose illustrated in FIG. 9.

Referring to FIG. 9, package/baggage inspection system 150 includes arotatable gantry 152 having an opening 154 therein through whichpackages or pieces of baggage may pass. The rotatable gantry 152 housesa high frequency electromagnetic energy source 156 as well as a detectorassembly 158 having arrays of integrated scintillator/collimator cellssimilar to that shown in FIG. 6 and fabricated using an assemblyapparatus similar to that described with respect to FIG. 7. A conveyorsystem 160 is also provided and includes a conveyor belt 162 supportedby structure 164 to automatically and continuously pass packages orbaggage pieces 166 through opening 154 to be scanned. Objects 166 arefed through opening 154 by conveyor belt 162, imaging data is thenacquired, and the conveyor belt 162 removes the packages 166 fromopening 164 in a controlled and continuous manner. As a result, postalinspectors, baggage handlers, and other security personnel maynon-invasively inspect the contents of packages 166 for explosives,knives, guns, contraband, etc.

The present invention has been described with respect to fabricating anintegrated scintillator and collimator for a CT based imaging system.Further, fabrication of a rectangular shaped scintillator/collimatorcombination has been described. However, the present inventioncontemplates additional patterns or shaped cells being fabricated.Additionally, the present invention envisions numerous collimatormaterial combinations beyond the tungsten/epoxy mixture previouslydescribed. Additionally, the high precision alignment and toolingaspects of the present invention may be used to support different“molding” processes such as extrusion, injection molding, and the like.The high precision alignment and tooling aspects could be also appliedto electronics packaging application to provide x-ray shielding ofsensitive components.

Additionally, the present invention has been described with respect toan integrated scintillator whereupon the collimator plates are castalong one dimensional, i.e., the z-axis. However, integratedscintillators and collimators may be formed using the aforementionedmethods of manufacturing along an x and z axis thereby rendering a“checkerboard” full two-dimensional (2D) arrangement of integratedscintillators and collimators. The present invention may be implementedto create a partial 2D array of integrated scintillator and collimators.That is, the collimator mold may be constructed such that the collimatorcavities have different heights when filled with the collimator mixture.As a result, the collimator plates along one axis, i.e., the z-axis, mayhave a greater height than collimator plates along another axis, i.e.,the x-axis.

Therefore, in accordance with one embodiment of the present invention, amethod of manufacturing a detector having an integrated scintillator andcollimator is provided. The method includes the steps of positioning anarray of scintillator elements or pack on a tooling base and positioninga collimator mold housing having a collimator mold cavity therein on theblock. As a result, the mold cavity will be very accurately aligned tothe scintillator array pattern. A collimator mixture is then disposedinto the mold cavity and allowed to cure to form an integratedscintillator and collimator.

In accordance with another embodiment of the present invention, adetector for a CT system includes an array of scintillation elementsarranged to convert received x-rays to light. A plurality of collimatorelements is integrally formed in a top surface of the array ofscintillation elements and operates to attenuate off-angle scatteredx-rays from being detected by scintillator elements. The detectorfurther includes an array of photodiode elements arranged to receivelight emissions from the array of scintillation elements.

According to another embodiment of the present invention, an integratedscintillator and collimator array is formed by the steps of placing anarray of pixilated scintillators on a tooling base and positioning acollimator mold defining a plurality of cavities that extend to a topsurface of the array adjacent the array. A collimator material is thendisposed within the plurality of cavities and cured so as to form theintegrated scintillator and collimator array.

In accordance with yet another embodiment of the present invention, anapparatus for manufacturing an integrated scintillator and collimatorincludes a tooling base designed to support a block of scintillatingmaterial and a mold to be positioned on the block of scintillatingmaterial. An alignment mechanism is provided to align the block in themold in an aligned arrangement as well as a mold evacuator designed toremove air cavities within the mold. A collimator mixture supply is alsoprovided to supply collimator material to the mold.

According to yet another embodiment of the present invention, a systemto manufacture an integrated scintillator/collimator includes means forpositioning a block of scintillator pack on a tooling base as well asmeans for positioning a collimator mold over the block. Means foraligning the block and the collimator mold is provided as well as meansfor removing air cavities from the mold. The system also includes meansfor disposing collimator material into a volume previously occupied bythe removed air cavities and means for curing the collimator material toform an integrated scintillator and collimator.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A method of manufacturing a detector having an integratedscintillator and collimator, the method comprising the steps of: forminga scintillator pack; and molding a collimator to the scintillator packto form an integrated scintillator and collimator.
 2. The method ofclaim 1 further comprising the step of milling a top reflector surfaceof the scintillator pack prior to molding the collimator to thescintillator pack.
 3. The method of claim 1 comprising the step offastening a collimator mold to the scintillator pack prior to the stepof molding the collimator mold having a plurality of cavities.
 4. Themethod of claim 3 further comprising the step of filling the moldcavities with a collimator mixture.
 5. The method of claim 4 furthercomprising the step of removing air from the collimator mold using avacuum pump prior to filling the mold cavities with the collimatormixture.
 6. The method of claim 4 wherein the collimator mixtureincludes a combination of tungsten and epoxy.
 7. The method of claim 3wherein the collimator mold includes a series of parallel-alignedcavities designed to receive a collimator mixture.
 8. The method ofclaim 3 wherein the collimator mold is formed of stainless steel.
 9. Adetector comprising: a scintillator having a 2D array of scintillationelements arranged to convert received x-rays to light; and a collimatorhaving either a 1D or a 2D array of collimator elements molded to anx-rays reception surface of the scintillator to collimate x-rays towardindividual scintillation elements.
 10. The detector of claim 9 whereineach of the collimator elements is fabricated from a tungsten/epoxycombination.
 11. The detector of claim 9 wherein the collimator elementsare arranged along two dimensions.
 12. The detector of claim 9incorporated into a CT imaging system.
 13. The detector of claim 12wherein the CT imaging system includes at least a medical scanner and aparcel inspection apparatus.
 14. A method of CT detector manufacture,the method comprising the step of molding a collimator directly to anx-ray reception surface of a scintillator.
 15. The method of claim 14wherein the step of molding includes the steps of: placing ascintillator having an array of scintillator elements on a tooling base;positioning a collimator mold having a plurality of cavities on thescintillator; filling the collimator mold cavities with a collimatorcomposition; and curing the collimator composition.
 16. The method ofclaim 15 further comprising the step of orienting the scintillator andthe collimator mold with respect to a set of pins and bore datums. 17.The method of claim 15 further comprising the step of removing air fromthe collimator mold cavities by vacuum pumping the air through anevacuation gate before the step of filling.
 18. The method of claim 15wherein the collimator composition includes tungsten and epoxy.
 19. Themethod of claim 18 wherein the tungsten has a powder form.